1. Field of the Invention
The invention relates to a modified resin, and more particularly to a modified bismaleimide resin, a preparation method thereof and a composition comprising the same.
2. Description of the Related Art
According to the implementation of the Restriction of Hazardous Substance (RoHS) Directive, using environmentally friendly materials has become a basic requirement. Although the Restrictions of the Hazardous Substance (RoHS) Directives of various nations are different, the substantial contents are similar. For example, most nations prohibit the use of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE). Thus, developments of green halogen-free copper clad laminate (CCL) materials and lead-free manufacturing processes are required. However, lead-free solder alloy has a higher melting point than that of conventional tin-lead solder, impacting circuit substrate materials and other auxiliary elements. While tin-lead solder has been replaced by a lead-free solder alloy, without other supporting measures, the reliability of the substrate has deteriorated. Thus, the development of substrate materials capable of bearing multiple high temperature manufacturing processes is required. During high temperature manufacturing processes, z-axis expansion and decomposition of substrate materials may occur. A high soldering temperature leads to an increased z-axis expansion of substrate materials, deteriorating through hole reliability. Also, substrate materials are easily decomposed during high-temperature soldering operations, deteriorating material properties, for example, increased moisture content, reduced glass transition temperature and deteriorated dielectricity. Thus, development of substrate materials with high thermal resistibility is currently desirable. The thermal resistibility is exhibited by glass transition temperature (Tg). Generally, higher glass transition temperature exhibits higher thermal resistibility of materials. Thus, development of halogen-free copper clad laminate (CCL) materials with high glass transition temperature is important to meet the requirement of halogen-free substrate materials and lead-free manufacturing processes.
Electronic end products with light weight, a thin profile, small volume, high computation speed and wireless ability are desirable. However, with reduced volume and increased computation speed, a great quantity of heat is produced. The reliability and lifetime of such products is reduced due to the overheating of integrated circuit elements as the heat gradually accumulates. Thus, achieving effective heat dissipation to maintain a stable system has become increasingly important. The main cause of damage or loss of function of electronic devices is high temperature rather than vibration, humidity or dust. Thus, the development of substrate materials with high thermal conductivity is desirable in the thermal management industry.
In a conventional halogen-free environmentally safe material composition, a phosphorus-containing flame retardant is substituted for the original halogen-containing flame retardant. However, while a phosphorus-containing flame retardant is utilized, inorganic powder must also be added to pass the UL-94V0 test. The inorganic powder may comprise hydroxides, for example silicon dioxide or aluminum hydroxide. However, while silicon dioxide is added, the hardness of the formed halogen-free substrate is increased. This is un-favorable because it makes it difficult to drill through the material during the later production phase. When aluminum hydroxide is added, the substrate liberates moisture at low temperature during heating processes. This makes it hard to pass the pressure cooker test (PCT). Currently, the glass transition temperature (Tg) of halogen-free epoxy resin copper clad laminate (CCL) materials merely achieves about 180° C. (less than 200° C. of materials highly thermal resistibility) measured by TMA.
Currently, BT resin developed in 1982 by Japan's Mitsubishi Gas Chemical Company and Bayer Chemical Company technical guidance is an environmentally safe material that is halogen-free and phosphorus-free with a maximum utilized quantity. BT resin polymerized by bismaleimide (B) and triazine (T) and possesses a high glass transition temperature (Tg) of 255-330° C., low dielectric constant and low dissipation factor. However, the brittleness and water absorption thereof is high. Although rigid BT resin has high thermal resistibility, the tensile strength thereof is low, resulting in poor processability. Also, the water absorption of the polar imide group of BT resin is high. Adding epoxy resins may overcome such drawbacks. However, the thermal resistibility thereof is consequently reduced (the glass transition temperature (Tg) thereof is reduced to 170-210° C.). Currently, the glass transition temperature (Tg) of the commercial BT resin substrate material achieves 210° C. above, for example those developed by Mitsubishi Gas Chemical (Tg of 210° C.) and Sumitomo Bakelite (Tg of 220° C.). Additionally, a BN resin-based substrate material with halogen-free, phosphorus-free and high glass transition temperature (Tg) is developed by Mitsui Chemical, with a glass transition temperature (Tg) of 300° C. (measured by DMA). However, adding aluminum oxide is also required to achieve UL-94 V0 test, for example US 2006/0084787A1 “Novel cyanate ester compound, flame-retardant resin composition, and cured product thereof” and US 2008/02621397A1 “Flame retardant crosslink agent and epoxy resin compositions free of halogen and phosphorous”.
A thermally cured bismaleimide (BMI) with high glass transition temperature (Tg) is popular. Although rigid BMI has highly thermal resistibility, the tensile strength thereof is low, resulting in poor processability. Some BMI modification methods have been addressed during the last 20 years. Although adding diamine can improve the mechanical properties and adhesion of BMI, the cost and processability thereof cannot meet the market requirements.